High purity polycrystalline silicon can be produced, for example, by a hydrogen reduction of trichlorosilane represented by the following formula (1), and a thermal decomposition of trichlorosilane represented by the following formula (2), using trichlorosilane (SiHCl3: referred to as TCS), silicon tetrachloride (SiCl4: referred to as STC) and hydrogen as raw materials:SiHCl3+H2→Si+3HCl  (1)4SiHCl3→Si+3SiCl4+2H2  (2)
Trichlorosilane used for a raw material of the producing method described above, is obtained by making metallurgical grade silicon react with hydrogen chloride, thereby producing crude trichlorosilane, and purifying this trichlorosilane by distillation. Furthermore, trichlorosilane can also be produced using silicon tetrachloride that is recovered by distillation separation from the discharged gas of a polycrystalline silicon-producing reaction, as a raw material, by a hydrogen-addition conversion reaction represented by the following formula (3):SiCl4+H2→SiHCl3+HCl  (3)
As an apparatus for producing this trichlorosilane, a conversion reaction apparatus (converter furnace) which is described in Patent Document 1 is known. This conversion reaction apparatus is provided with a reaction chamber having a double-chamber consisting of an outer chamber and an inner chamber formed by two concentric tubes surrounded by a heating element, and a heat exchanger disposed below this reaction chamber. Furthermore, a raw material gas supply pipeline that supplies hydrogen and silicon tetrachloride to the reaction chamber, and a discharge pipeline that discharges the reaction product gas from the reaction chamber are connected to each other through the heat exchanger. In the heat exchanger, the supply gas that is supplied to the reaction chamber is preheated as heat is transferred from the reaction product gas discharged from the reaction chamber, and at the same time, the supply gas cools the discharged reaction product gas.
Furthermore, Patent Document 2 discloses that a reaction product gas containing trichlorosilane and hydrogen chloride is obtained by introducing silicon tetrachloride and hydrogen into a reaction chamber, and subjecting the components to a conversion reaction at a temperature of 600° C. to 1200° C. As a producing apparatus for trichlorosilane, an apparatus provided with a cooling unit which rapidly cools the reaction product gas discharged from the reaction chamber, at a cooling rate such that, for example, the temperature reaches 300° C. or below within 1 second, is suggested.